C-terminal truncated hepatitis B virus X protein promotes hepatocarcinogenesis through enhanced stemness and resistance to therapy

Abstract

Tumor relapse after chemotherapy typifies hepatocellular carcinoma (HCC) and is believed to be attributable to residual cancer stem cells (CSCs) that survive initial treatment. Chronic infection with hepatitis B virus (HBV) has long been linked to the development of HCC. Upon chronic infection, random HBV genome integration can lead to truncation of hepatitis B virus X (HBx) protein at the C-terminus. The resulting C-terminal-truncated HBx (HBx-ΔC) was previously shown to confer enhanced invasiveness and diminished apoptotic response in HCC cells. In this study, we found HBx-ΔC to be more frequently detected in HCC clinical samples than their matched non-tumor counterparts. In addition, we also identified a strong positive correlation between HBx-ΔC and the liver cancer stem cell marker CD133, in a panel of liver cell line tested. Subsequently, we delineated the role of a naturally occurring HBx-ΔC (HBx-Δ14) in promoting stemness and aggressive behaviors in HCC cells. The stable overexpression of HBx-Δ14 in HCC cell line (Huh7) and immortalized normal liver cell line (MIHA) promoted expression of stemness markers, EpCAM and SOX2. In vitro functional studies with HBx-Δ14 stably overexpressed in Huh7 demonstrated an increased ability to self-renew, resist chemotherapy (5-fluorouracil) and targeted therapy (sorafenib), migrate and induce capillary tube formation in endothelial cells. Similar functional results were also obtained when HBx-Δ14 was stably overexpressed in MIHA cells. Taken together, in addition to its role in enhancing HCC metastasis, we find HBx-Δ14 to confer cancer and stem cell-like features in HCC, and to play an important role in driving tumor relapse in this deadly disease.